The present invention generally pertains to the reproduction of binary signals from a recording medium and is particularly directed to a system for reproducing such signals when they are read from the recording medium at varying speeds.
A magnetic recording medium is commonly used for recording binary signals. The signals are recorded by effecting alternating flux changes in the recording medium. In accordance with the particular binary coding scheme being employed, the distance of separation between consecutively effected flux changes typically is either a first predetermined distance or a second predetermined distance. Two popular binary coding schemes are pulse width modulation and F2F.
In accordance with the pulse width modulated binary coding scheme, a flux change in one direction (to wit: South-to-North) represents a clock pulse and a flux change in the opposite direction (North-to-South) represents a data pulse. The distance of separation between the South-to-North flux changes representing clock pulses is constant and the distance of separation from the South-to-North flux changes (representing clock pulses) to the North-to-South flux changes (representing data pulses) is either a first predetermined distance to represent one binary state or a second predetermined distance that is less than the first predetermined distance to represent the opposite binary state.
In accordance with the F2F binary coding scheme, one binary state is represented by two consecutive flux changes that are separated by a first predetermined distance, and the opposite binary state is represented by three consecutive flux changes that are separated by a second predetermined distance that is approximately half the first predetermined distance.
To reproduce the recorded binary signal the recording medium is moved in relation to a read head which senses the flux changes in the recording medium and produces an electrical signal which is amplified and provided to a signal processing circuit. The recording medium is moved past the read head at a relatively constant speed such that the duration between the signals produced by the read head that are received by the signal processing circuit represent the distances between the flux changes in the recording medium, thereby enabling the recorded binary signal to be reproduced in accordance with the binary coding scheme employed for recording.
In some applications, however, this system for reproducing recorded binary signals is not satisfactory. For example, binary signals are frequently recorded in magnetic recording medium strips affixed to plastic cards, such as credit cards and bank cards. When these cards are transported past a read head at a relatively constant speed they can be read satisfactorily. However, mechanisms for transporting the recording medium past the read head at a constant speed add to the cost of a device to be used by merchants and others for reading binary data from such cards. And, although the flux changes can be sensed by moving the card past a read head by hand, the variation in the speed of such hand movement makes it impossible to consistently reproduce the recorded binary signal accurately with conventional binary signal reproducing systems.
Therefore it is an object of the present invention to provide a system for reproducing binary signals from a recording medium wherein the recording medium may be read at varying speeds as well as at constant speeds.